In known electro-hydraulic control systems, a series of roof supports together with their associated hydraulically operated devices are disposed alongside a mineral face and each support has a control unit with a programmable electronic device, such as a microprocessor, used to actuate electromagnetic valves to operate the devices in some desired sequence.
Electro-hydraulic control systems are known in various versions (see "Gluckauf", 1981, pp. 1155-1162; "Gluckauf", 1984, pp. 135-140; "Gluckauf", 1986, pp. 543-552 and "Gluckauf", 1986, pp. 1183-1187). The systems in which an individual electronic control unit with its microprocessor is allocated to each support of the longwall working with all the individual control units being coupled with one another and possibly with a central control appliance through a data transmission link, the so-called "system bus", have proved their value in practice. The individual control units are usually provided with an operating keyboard, with the aid of which the various control operations (individual control actions, automatic flow control actions, sequence control actions) can all be initiated. The control system is also expediently supplied on a de-centralized basis with power at an intrinsically safe level. Also in the known electro-hydraulic control systems the electromagnetic valves are assembled as blocks or valve units associated with the individual supports. Each block may comprise a relatively large number of electromagnetic valves, not infrequently twenty or more, which must be electrically actuated individually or in groups by the associated control unit for the execution of the various control operations. This requires a very large number of electrical connections between the control unit and the valve unit. If the heavy valve unit is arranged spatially separately from the associated control unit, then for the production of the electrical connections it is necessary to provide a very large number of electrical conductors or a cable with a large number of electric cores.
It is a general object of the invention to reduce the number of the electrical connections to be produced between each control unit and its associated valve unit, preferably in such a way that in the case of spatial separation of the valve unit from the associated electronic control unit the electrical connection can be brought about with the aid of a cable having a maximum of four conductor cores.